express-prom-bundle
v8.0.0
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express middleware with popular prometheus metrics in one bundle
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express prometheus bundle
Express middleware with popular prometheus metrics in one bundle. It's also compatible with koa v1 and v2 (see below).
This library uses prom-client v15+ as a peer dependency. See: https://github.com/siimon/prom-client
If you need a support for older versions of prom-client (v12-v14), downgrade to express-prom-bundle v6.6.0
Included metrics:
up
: normally is just 1http_request_duration_seconds
: http latency histogram/summary labeled withstatus_code
,method
andpath
Install
npm install prom-client express-prom-bundle
Sample Usage
const promBundle = require("express-prom-bundle");
const app = require("express")();
const metricsMiddleware = promBundle({includeMethod: true});
app.use(metricsMiddleware);
app.use(/* your middleware */);
app.listen(3000);
- call your endpoints
- see your metrics here: http://localhost:3000/metrics
ALERT!
The order in which the routes are registered is important, since only the routes registered after the express-prom-bundle will be measured
You can use this to your advantage to bypass some of the routes. See the example below.
Options
Which labels to include in http_request_duration_seconds
metric:
- includeStatusCode: HTTP status code (200, 400, 404 etc.), default: true
- includeMethod: HTTP method (GET, PUT, ...), default: false
- includePath: URL path (see important details below), default: false
- customLabels: an object containing extra labels, e.g.
{project_name: 'hello_world'}
. Most useful together with transformLabels callback, otherwise it's better to use native Prometheus relabeling. - includeUp: include an auxiliary "up"-metric which always returns 1, default: true
- metricsPath: replace the
/metrics
route with a regex or exact string. Note: it is highly recommended to just stick to the default - metricType: histogram/summary selection. See more details below
- httpDurationMetricName: Allows you change the name of HTTP duration metric, default:
http_request_duration_seconds
.
metricType option
Two metric types are supported for http_request_duration_seconds
metric:
Additional options for histogram:
- buckets: buckets used for the
http_request_duration_seconds
histogram
Additional options for summary:
- percentiles: percentiles used for
http_request_duration_seconds
summary - ageBuckets: ageBuckets configures how many buckets we have in our sliding window for the summary
- maxAgeSeconds: the maxAgeSeconds will tell how old a bucket can be before it is reset
- pruneAgedBuckets: When enabled, timed out buckets will be removed entirely. By default, buckets are reset to 0.
Transformation callbacks
- normalizePath:
function(req)
orArray
- if function is provided, then it should generate path value from express
req
- if array is provided, then it should be an array of tuples
[regex, replacement]
. Theregex
can be a string and is automatically converted into JS regex. - ... see more details in the section below
- if function is provided, then it should generate path value from express
- urlValueParser: options passed when instantiating url-value-parser. This is the easiest way to customize which parts of the URL should be replaced with "#val". See the docs of url-value-parser module for details.
- formatStatusCode:
function(res)
producing final status code from expressres
object, e.g. you can combine200
,201
and204
to just2xx
. - transformLabels:
function(labels, req, res)
transforms the labels object, e.g. setting dynamic values to customLabels - urlPathReplacement: replacement string for the values (default: "#val")
Other options
autoregister: if
/metrics
endpoint should be registered (default: true)promClient: options for promClient startup, e.g. collectDefaultMetrics. This option was added to keep
express-prom-bundle
runnable using confit (e.g. with kraken.js) without writing any JS code, see advanced examplepromRegistry: Optional
promClient.Registry
instance to attach metrics to. Defaults to globalpromClient.register
.metricsApp: Allows you to attach the metrics endpoint to a different express app. You probably want to use it in combination with
autoregister: false
.bypass: An object that takes onRequest and onFinish callbacks that determines whether the given request should be excluded in the metrics. Default:
{ onRequest: (req) => false, onFinish: (req, res) => false }
onRequest
is run directly in the middleware chain, before the request is processed.onFinish
is run after the request has been processed, and has access to the express response object in addition to the request object. Both callbacks are optional, and if one or both returns true the request is excluded.As a shorthand, just the onRequest callback can be used instead of the object.
More details on includePath option
Let's say you want to have latency statistics by URL path,
e.g. separate metrics for /my-app/user/
, /products/by-category
etc.
Just taking req.path
as a label value won't work as IDs are often part of the URL,
like /user/12352/profile
. So what we actually need is a path template.
The module tries to figure out what parts of the path are values or IDs,
and what is an actual path. The example mentioned before would be
normalized to /user/#val/profile
and that will become the value for the label.
These conversions are handled by normalizePath
function.
You can extend this magical behavior by providing
additional RegExp rules to be performed,
or override normalizePath
with your own function.
Example 1 (add custom RegExp):
app.use(promBundle({
normalizePath: [
// collect paths like "/customer/johnbobson" as just one "/custom/#name"
['^/customer/.*', '/customer/#name'],
// collect paths like "/bobjohnson/order-list" as just one "/#name/order-list"
['^.*/order-list', '/#name/order-list']
],
urlValueParser: {
minHexLength: 5,
extraMasks: [
'ORD[0-9]{5,}' // replace strings like ORD1243423, ORD673562 as #val
]
}
}));
Example 2 (override normalizePath function):
app.use(promBundle(/* options? */));
// let's reuse the existing one and just add some
// functionality on top
const originalNormalize = promBundle.normalizePath;
promBundle.normalizePath = (req, opts) => {
const path = originalNormalize(req, opts);
// count all docs as one path, but /docs/login as a separate one
return (path.match(/^\/docs/) && !path.match(/^\/login/)) ? '/docs/*' : path;
};
For more details:
- url-value-parser - magic behind automatic path normalization
- normalizePath.js - source code for path processing
Example 3 (return express route definition):
app.use(promBundle(/* options? */));
promBundle.normalizePath = (req, opts) => {
// Return the path of the express route (i.e. /v1/user/:id or /v1/timer/automated/:userid/:timerid")
return req.route?.path ?? "NULL";
};
express example
setup std. metrics but exclude up
-metric:
const express = require("express");
const app = express();
const promBundle = require("express-prom-bundle");
// calls to this route will not appear in metrics
// because it's applied before promBundle
app.get("/status", (req, res) => res.send("i am healthy"));
// register metrics collection for all routes
// ... except those starting with /foo
app.use("/((?!foo))*", promBundle({includePath: true}));
// this call will NOT appear in metrics,
// because express will skip the metrics middleware
app.get("/foo", (req, res) => res.send("bar"));
// calls to this route will appear in metrics
app.get("/hello", (req, res) => res.send("ok"));
app.listen(3000);
See an advanced example on github
koa v2 example
const promBundle = require("express-prom-bundle");
const Koa = require("koa");
const c2k = require("koa-connect");
const metricsMiddleware = promBundle({/* options */ });
const app = new Koa();
app.use(c2k(metricsMiddleware));
app.use(/* your middleware */);
app.listen(3000);
using with cluster
You'll need to use an additional clusterMetrics() middleware.
In the example below the master process will expose an API with a single endpoint /metrics
which returns an aggregate of all metrics from all the workers.
const cluster = require('cluster');
const promBundle = require('express-prom-bundle');
const promClient = require('prom-client');
const numCPUs = Math.max(2, require('os').cpus().length);
const express = require('express');
if (cluster.isMaster) {
for (let i = 1; i < numCPUs; i++) {
cluster.fork();
}
const metricsApp = express();
metricsApp.use('/metrics', promBundle.clusterMetrics());
metricsApp.listen(9999);
console.log('cluster metrics listening on 9999');
console.log('call localhost:9999/metrics for aggregated metrics');
} else {
new promClient.AggregatorRegistry();
const app = express();
app.use(promBundle({
autoregister: false, // disable /metrics for single workers
includeMethod: true
}));
app.use((req, res) => res.send(`hello from pid ${process.pid}\n`));
app.listen(3000);
console.log(`worker ${process.pid} listening on 3000`);
}
using with kraken.js
Here is meddleware config sample, which can be used in a standard kraken.js application. In this case the stats for URI paths and HTTP methods are collected separately, while replacing all HEX values starting from 5 characters and all IP addresses in the path as #val.
{
"middleware": {
"expressPromBundle": {
"route": "/((?!status|favicon.ico|robots.txt))*",
"priority": 0,
"module": {
"name": "express-prom-bundle",
"arguments": [
{
"includeMethod": true,
"includePath": true,
"buckets": [0.1, 1, 5],
"promClient": {
"collectDefaultMetrics": {
}
},
"urlValueParser": {
"minHexLength": 5,
"extraMasks": [
"^[0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+$"
]
}
}
]
}
}
}
}
License
MIT